The following 3 methods are known as examples of the conventional betaine recovery methods.
A method (1) is one as disclosed in claim 1 of Japanese Patent Publication No. 50,895/1990 wherein diluted molasses having a solids content of 20 to 50 wt. % is batchwise passed through a chromatographic column packed with a strongly acidic cation exchange resin (crosslinked with 2 to 12 wt. % of divinylbenzene) in the form of an alkaline metal salt at a resin bed height of 2.5 to 10 m to recover a betaine fraction (see the flow chart of FIG. 2 for further particulars).
A method (2) is one as disclosed in claims 2 and 3 of Japanese Patent Publication No. 50,895/1990 wherein a crude betaine solution (betaine fraction) obtained according to the foregoing method of claim 1 is batchwise passed through the foregoing chromatographic column (claim 2) to recover a higher-purity betaine fraction while a lower-purity betaine fraction obtained at this time is also separately recovered and recirculated (claim 3) to recover betaine in this fraction as well (see the flow chart of FIG. 3 for further particulars).
A method (3) is one as disclosed in Proceedings of the Research Society of Japan Sugar Refineries' Technologists, Vol. 41 pp. 29-36 (1993) wherein molasses produced in a beet sugar factory where a method of manufacturing sucrose by ion exchange refining is adopted is separated with a multi-component separation simulated moving bed chromatographic separator to recover betaine (see the flow chart of FIG. 4 for further particulars).
The foregoing conventional methods of recovering betaine are all used for a solution having a comparatively low salts concentration with no consideration given to the fact that the ionic form of the cation exchange resin is changed by salts.
However, waste produced in the course of separation and recovery of sucrose from sugar beet extract or sugar beet molasses with a 2-component separation simulated moving bed chromatographic separator using a strongly acidic cation exchange resin in a salt form as chromatographic packing contains 5-20 wt. % sucrose, 40-75 wt. % salts, 5-20 wt. % betaine, 1-10 wt. % monosaccharides and 0.5-5 wt. % unknown substances based on solids (i.e., based on dry solids). Thus, when this waste is concentrated to a solids content of about 50% (weight/solution weight), the salts concentration of the resulting concentrate becomes several in normality.
When such salts-rich waste derived from a plant (e.g., beet) or its concentrate is passed as a starting solution material through a chromatographic column packed with a cation exchange resin, 40 to 80% of the ionic form of the cation exchange resin becomes the K form because of a large amount of potassium ions existing in the starting solution material, thus leading to poor separation of betaine from monosaccharides such as glucose, fructose and inositol, and other unknown substances. Accordingly, there inevitably arises a problem that high-purity betaine cannot be obtained by chromatographic separation wherein a cation exchange resin is used as chromatographic packing.
For example, the partition coefficients of components in the starting solution material by a strongly acidic cation exchange resin Amberlite (registered trademark) CR-1320 for chromatographic separation (manufactured by Rohm and Haas Company) in an ionic form equilibrated with that of residual waste produced after recovery of sucrose from a certain sugar beet molasses are 0.19 for salts, 0.24 for trisaccharides, 0.30 for sucrose, 0.39 for unidentified disaccharides, 0.45 for glucose, 0.47 for betaine, 0.51 for a fructose+inositol mixture, 0.54 for unidentified monosaccharides, and 0.59 for unknown substances (impurities believed to be nucleic acids, etc.) other than saccharides in the eluting (outflowing) order. Thus, it has been understood that the simulated moving bed procedure of separation of 2 components can separate betaine from salts, trisaccharides, sucrose, and unidentified disaccharides, but involves a difficulty in separating betaine from monosaccharides and unknown substances. Incidentally, the ionic form composition (based on ion exchange capacity) of the cation exchange resin in this case has turned out to consist of 26% Na form, 73% K form and 1% Ca form. Poor separation is of course inferable from these values of partition coefficients. This was substantiated from the fact that the betaine purity was only at most about 82% based on solids (in terms of areal percentage in high-performance liquid chromatography using a sodium-form ion exchange column and a differential refractometer) even with a simulated moving bed chromatographic separator best in separating efficiency in Comparative Example 1 described later.
Accordingly, an object of the present invention is to provide a process for recovering high-purity betaine from either waste having a high salts concentration in the solids-based composition thereof and produced in the chromatographic separation procedure in the beet sugar industry or its concentrate.